Problem: William just found beautiful yarn for 20 percent off at his favorite yarn store. He can make 1 scarf from $\frac{2}{5}$ of a ball of yarn. If William buys 8 balls of yarn, how many scarves can he make?
We can divide the balls of yarn (8) by the yarn needed per scarf ( $\frac{2}{5}$ of a ball) to find out how many scarves William can make. $ \dfrac{{8 \text{ balls of yarn}}} {{\dfrac{2}{5} \text{ ball per scarf}}} = {\text{ number of scarves}} $ Dividing by a fraction is the same as multiplying by the reciprocal. The reciprocal of ${\dfrac{2}{5} \text{ ball per scarf}}$ is ${\dfrac{5}{2} \text{ scarves per ball}}$ $ {8\text{ balls of yarn}} \times {\dfrac{5}{2} \text{ scarves per ball}} = {\text{ number of scarves}} $ ${\dfrac{40}{2}\text{ scarves}} = 20\text{ scarves}$ William can make 20 scarves.